TOWMASTER User Manual Version : 1.0.0 Date : 23-November-2014
License Information TOWMASTER TOWMASTER software and source code are property of Technomak Offshore & Marine Consultancy. The software along with this user manual allows the purchaser to use the software for commercial and non-commercial purpose. DISCLAIMER OF WARRANTY Neither Technomak Offshore & Marine Consultancy (and its group of companies), nor the author of this program and documentation are liable or responsible to the purchaser or user for loss or damage caused, or alleged to be caused, directly or indirectly by the software and its attendant documentation, including (but not limited to) interruption on service, loss of business, or anticipatory profits. Page 2 of 25
Contents _ License Information... 2 About TOWMASTER... 4 TOWMASTER Analysis Methodology... 5 Range of Validity... 5 Unit System... 5 TOWMASTER Inputs... 5 TOWMASTER Resistance Calculation... 13 TOWMASTER Results... 14 Limitations... 14 References... 15 Appendix 1.1 - Example 1... 16 Page 3 of 25
About TOWMASTER TOWMASTER is designed for ios platforms and available on iphone and ipads. This manual gives step by step procedure to use the software, which can be used to estimate the bollardpull requirement for towing tugs. TOWMASTER includes recognized methods (DNV Guidelines for Marine Operations, Bureau Veritas and tow tested results) for estimation of resistance and bollardpull. You can download and install TOWMASTER from App Store. Page 4 of 25
TOWMASTER Analysis Methodology Present version of TOWMASTER has two independent methods to predict the barge resistance and tug bollardpull during tow. The present version uses the following methods for resistance and bollard pull prediction. Bureau Veritas Towage of Sea Vessels or Floating Units Resistance of Offshore Barges and Required Horse Power (OTC Paper 3320) Both the methods are suitable for the conventional material barge tow and give comparable results. However, it should be noted that none of the resistance prediction methods are exact and can vary depending on the hull form parameters, tug parameters and environment parameters. Range of Validity Below range of validity may be used as a guideline to verify the accuracy of the results. However, slight variations in outside the below parameters are also found to give reliable results. METHOD Cb V/ L OTC ~0.90 0.0-0.4 BV ~0.90 0.0-0.4 Unit System Current version of TOWMASTER uses meter-metric Tons. TOWMASTER Inputs Main input sheets for TOWMASTER is similar to the below. The user interface may vary depending on the platform and equipment (ipad or iphone). Page 5 of 25
Input Sheet Hull Parameters Page 6 of 25
Hull Appendages Set Tow Conditions Definition of input parameters is as below. Job Name Your project name or job name. This will be printed in the output file. Device Name This field is auto populated with your device name by default. User may change it as required. Page 7 of 25
Hull Parameters The for hull parameters, which are as below. button will take you to the input sheet Length WL Length of waterline in meters. Beam Mld Moulded breadth in meters. Depth Mld Moulded depth in meters Draft Fwd Mld Froward Draft (mld) in meters Draft Aft Mld Aft Draft (mld) in meters Displacement Floating displacement in metric tones of 1000 kg. Wet Surface Area Wetted surface area of the hull. If not known, leave blank. The program uses the following equation to calculate the wetted surface area, which holds good for barges (Ref 3). WWWWWW = 0.92 LLLLLL(BB + 1.81 TT) Where, LWL is the length of waterline, Page 8 of 25
B is the Beam (Mld) T is the Mean Draft Cargo Wind Area This is the windage area of the cargo on the barge in m 2. Area Center abv wl This is the elevation of center of pressure of the windage area above mean sea level. The wind speed at 10m above mean sea level will be scaled to the actual elevation as per DNV-RP-C205. Shape Factor Shape Factor for the material barge. It ranges from 750 for a shaped bow to 1000 for rectangular box. Average value of 850 is used as default. Service Allowance This is the increase in resistance due to unaccounted factors. A default allowance of 10% is consided. Days since drydock This will determine the increase in resistance due to fouling and marine growth. Default value is 730 days (2 years). Based on the actual number of days, the hull roughness is increased as per BV guidelines. Hull Appendages Clicking the button takes the user to the Appendages when applicable appendage area and form factors can be set. The Appendage view has various appendages such as Skeg, Bilge Keel, Other Appendage #1 and Other Page 9 of 25
Appendage #2. The button next to the appendage has the format of A=xx, f=yy (stands for Area (m2) = xx and form factor = yy). Clicking the individual button will take you to the appendage edit page where you can modify the appendage area and form factors. If you do not know the form factors, leave the default values or refer the note (see below snapshot). Clicking Done will update the Appendage Areas. Clicking the button will take you to the tow condition settings view. By default a STALL and TOW conditions area provided. Page 10 of 25
The default values for STALL condition are as per the Noble Denton Guidelies for Marine Transportation. User may change the values as required. TOW condition is the fair weather tow condition by default. Other parameters are as below. Significant Wave Height This is the significant wave height for stall and tow condition. Default value for STALL condition is as per major Marine Warranty Guidelines. However, user may change this as per the weather data for the tow route and required tow speed for normal tow conditions. Current Speed Surface current speed in m/s. It is assumed that the current speed is constant over the draft and surface current is conservatively used to estimate the drag force on the underwater hull. Wind Speed This is the design wind speed for the tow route at 10m above waterline. Normally a 1 hour mean wind speed may be considered for tow condition. Start Speed, End Speed and Speed Increment The required start, end and incremental speed for with bollardpull is to be calculated. Program Settings Below screen gives the program settings. Properties of seawater (specific gravity and kinematic viscosity) and air (specific gravity) are as per standards. Tug efficiency is as per DNV Rules for Planning and Execution of Marine Operations. Some guideline recommends tug efficiency as a function of bollardpull of towing tug (such as Noble Denton). In such cases, the user is requested to modify the tug efficiency manually based on the available tug. By default, both the bollardpull calculation methods are selected. Page 11 of 25
Icons and Symbols Click to run the bollardpull calculations. Immediately after completion of calculations, user will be taken to the Report View, where user can review the report and email as required. Click the Email Icon on the Report View to email the result. Page 12 of 25
To display this User Manual, click clicking the Email Icon below the user manual.. User can email the User Manual by Click at any stage to go back to the previous screen. TOWMASTER Resistance Calculation Total resistance is expressed as sum of frictional, residuary, appendage, wind and sea resistance. R t Total resistance expressed as (Rf + R r + R appendage + R wind + R curr + R wave ) x Service factor R Frictional Resistance. Frictional resistance is calculated as per ITTC 1957 f R R R R r appendage wind sea Residuary Resistance. Calculated as per the specific curves provided as per BV and OTC Paper 3320 (Ref 3 & 4) Appendage Resistance, based on form factors as per Holtrop & Mennen 82 (Ref 5, 6) Wind resistance expressed as ρρ. AA wwwwwwww. VV 2. CC ww., where V is the wind speed at center of windage area. Note that the wind speed input is the wind speed at 10m elevation, which is transferred to wind speed at desired height based on DNV- RP-C205. Sea resistance is calculated in accordance with DNV guidelines. Page 13 of 25
TOWMASTER Results TOWMASTER results include list of all input data for the vessel, cargo, environmental data and area and form factor of appendages. Information on the range of validity is also printed. The calculation results include the individual component of resistance for frictional, residuary, appendage, wind, sea resistance, total resistance and estimated bollard pull for each of the analysis method and environment condition selected. NOTE: In some cases, it may happen that the bollardpull for TOW is more than the STALL condition and available tug bollardpull is only adequate for Stall condition. The effect of this will be a reduced tow speed at normal tow, which may be acceptable based on operational requirements. Limitations 1. TOWMASTER is capable of calculating the bollardpull for conventional material barges under tow and not intended for higher Froude numbers (V/ L> 0.4). 2. The methodology is limited to conventional barges and shall not be used for other than material barges under tow (such as drill ships, fast crafts, slender hulls etc.) Page 14 of 25
References 1 Det Norske Veritas - Rules for Planning and Execution of Marine Operation 2. Noble Denton - General Guidelines for Marine Transportation (0030/ND) 3. Bureau Veritas - Towage at Sea of Vessels or Floating Units 4. Offshore Technology Conference (OTC) Paper #3320 - Resistance of Offshore Barges and Required Horse Power 5. J.Holtrop - A Statistical Re-Analysis of Resistance and Propulsion Data, 1984 6. J.Holtrop & G.G.J Mennen An Approximate Power Prediction Method, International Shipbuilding Progress,1982 7. Det Norske Veritas Environmental Conditions and Environmental Loads (DNV-RP- C205) Page 15 of 25
Appendix 1.1 - Example 1 Page 16 of 25
Objective : To find out bollardpull requirement of a barge with following dimensions. The barge has a jacket of frontal windage area of 500m2. LWL = 76.2m Beam Mld = 27.4m Depth Mld = 4.88m Draft Aft = 2.3m Draft Fwd = 1.7m Displacement = 3760MT Wetted Surface Area = Unknown Shape Factor = Default Windage area of jacket = 500m2 Center of pressure of wind area = 25m Skeg area = 20m2 Page 17 of 25
Input screen for the problem above is shown here. Page 18 of 25
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Output of Example-1 Page 21 of 25
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